Agreed.

First of all run them all through a chute and weigh (if you can) and eartag all cows and calves to make a data base in Cattlemax. Observe the herd to line up what current calf eartag is nursing what cow eartag to establish pairs in Cattlemax.

Get any/all current bulls or bull calves out of there now and sell them. This first chute run is a good time to sort the bulls and bull calves off. They'll bring good money right now, the sooner the better. 

I wouldn't be in a hurry to sell the current cows regardless of their color. They are a locally adapted group to their location and conditions.

Focus on new bull(s). Use the money from selling current bulls and bull calves to buy one or more good virgin black bulls, one young bull for each 20-25 cows or yearling heifers.

For central Michigan I'd put the bull(s) in on July 15 for start of calving April 23, 2027.  Leave the bull(s) in for about 50 days. Then pull your bulls.

Sell any cows and their calves that calve after about May 15 as pairs. This leaves the remaining cows open for breeding when you put your bulls in.

This method will get your herd calving date moved to a good spring date for Michigan. Then you can start culling by selling any cows that don't calve by about June 15th  2027. I would look at transitioning to an all-black herd as a multiyear project. Focus on getting calving date straightened out and using good young bull(s) first.

JMHO. Good luck, should be fun!